Method for extracting copper from an aqueous solution

ABSTRACT

The invention relates to a method for extracting copper in liquid-liquid solvent extraction from aqueous solutions with a high sulphate content, by raising the viscosity of the extraction solution and by dispersing the aqueous solution into drops, achieving a dense drop aggregation. The viscosity of the extraction solution may be raised either by increasing the content of the actual extractant, the extraction reagent, in the extraction solution or by using a diluting agent with a higher viscosity than that of the diluting agent normally used. By raising the viscosity of the extraction solution the mixing durability of the extraction dispersion can be increased and resulting of that the amount of residual drops is decreased. Other advantages are that the extraction solution flow of the extraction process decreases in relation to the flow of the aqueous solution acting as the copper source and that the size of the extraction equipment needed is reduced.

The present invention relates to a method for extracting copper inliquid-liquid solvent extraction from aqueous solutions with a highsulphate content, by raising the viscosity of the extraction solutionand by dispersing the aqueous solution into drops, achieving a densedrop aggregation. The viscosity of the extraction solution may be raisedeither by increasing the content of the actual extractant, theextraction reagent, in the extraction solution or by using a dilutingagent with a higher viscosity than that of the diluting agent normallyused. By raising the viscosity of the extraction solution the mixingdurability of the extraction dispersion can be increased and resultingof that, the amount of residual drops is decreased. Other advantages arethat the extraction solution flow of the extraction process decreases inrelation to the flow of the aqueous solution acting as the copper sourceand that the size of the extraction equipment needed is reduced.

Dilute aqueous solutions form when poor copper ores are leacheddirectly. The copper content of such solutions is usually of the orderof 1-4 g/l Cu. In addition neutral salts often accumulate in thesolution, mainly aluminium and magnesium sulphates. Although the coppercontent does not rise above 1.5 g/l, the sulphate content may rise above40 g/l, to between 40 and 120 g/l. Some of the sulphate may originatefrom the ore or the possible use of seawater. In the extraction processthe aqueous solution is in a cycle between the extraction and theleaching and thus gradually accumulates the salts which raise theviscosity. Neutral salts can easily cause a viscosity increase harmfulto the aqueous solution, even 3 cP, which also disturbs the dispersingof the aqueous and extraction solutions and results in high amounts ofresidual drops. In particular when dispersion is desired where theorganic solution is continuous and the water in drops, an increasedviscosity in the aqueous solution can make it difficult to achieve sucha dispersion. Previously the increased viscosity caused by neutral saltsand the resulting disadvantages were not taken into account.

In copper extracting processes a mixed organic extraction solution andaqueous solution is generally used in the ratio of O/A (organic/aqueous)1.0-1.2. Present-day copper extracting processes usually followrecommendations given by extractant manufacturers, according to whichthe organic and aqueous solution of the extraction O/A ratio at allextraction stages of the extraction process should be of the order of1.0, and the extractant content raised to 3.3-4.2 vol. % per every gramof copper, which comes in the direction of flow of the first extractionstage of extraction. In practice this means that if the Cu content ofthe aqueous solution is 1.5 g/l, the extractant content is maximum 6.3vol. % according to the recommendations. Generally, when the amount ofcopper in the solution increases, the amount of extractant decreasesrelatively. The type of extractant is a chelating copper complexingagent, usually hydroxyoxyme, which forms a strong complex with copper,and one fact affecting the progress of copper extraction is how muchextractant is present in relation to the amount of copper to beextracted.

Generally, alifatic or aromatic hydrocarbons, kerosenes, with adistillation range between 190-245° C. are used as the diluting agentfor the copper extractant The viscosity of these substances is usuallybelow 2 cP, and for aromatics even below 1.5 cP. It is also possible tous mixtures of aromatic and alifatic hydrocarbons as the diluting agent,where the aromatic content of the mixture is around 20-30 vol. %.

As previously stated, in copper extraction it is difficult to get adispersion of an aqueous solution with a high sulphate content, minimum40 g/l, where the organic phas is continuous and the aqueous solution indrops, although this is essential in order to improve extractionperformance. According to th present invention, the viscosity of theextraction solution is now raised to the area of 3-11 cP, and this takesplace either by raising the extractant content or by using a dilutingagent with a high viscosity in the extraction solution. In addition tothis, that the organic phase has been made continuous, the method hasproved to have many other advantageous consequences. The essentialfeatures of the invention will become apparent in the attached patentclaims.

A rise in the viscosity of the extraction solution clearly raises themixing durability of the extraction dispersion. In this connection amixing-durable dispersion means a dispersion where no drops below 0.2 mmappear when the mixing intensity is max. 0.15 kWh/m³ in a mixing volumeof 50 m³. Volume-specific mixing power is dependent on the mixing volumeso that the power required decreases slightly as the volume increases.Obviously the mixing itself also affects mixing durability. The mixersdescribed in U.S. Pat. No. 5,185,081 have been settled on to use in themethod according to the present invention. These mixers have a doublehelix, which helps to avoid locally increasing shear rate forces and thesmall drops generated as a result. When the viscosity of the organicphase has been raised according to the invention and the extractiondispersion made heavier and this dispersion combined with a very smooth,thoroughly uniform mixing of controlled intensity in the mixing area,the conditions are achieved where an evenly distributed mixing energy isnot sufficient to attain a turbulence to form droplets. An evenlyattenuated mixing creates a dispersion where the drop size is uniformand which thus possesses good separation characteristics. Since theamount of residual drops is small, the extraction result is clearlyimproved.

In addition to the increase in viscosity of the extraction solution,another key factor is the mixing ratio of the solutions. The denser thedrop aggregation, the heavier and simultaneously more mixing-durable thedispersion. The most advantageous result is obtained when a dispersionis formed, where the extraction solution is continuous and the amount ofwater drops is raised.

When the viscosity of the extraction solution is raised, it has beenfound that an extraction solution with a higher viscosity is better ableto keep a larger amount of the aqueous solution than normal inside it asdrops. In the method according to our invention it is possible to lowerthe O/A ratio to between 0.7-1.0 without endangering the continuity ofthe extraction solution. In practice, this means that the extractionsolution flow can be reduced in relation to the copper-containing feedsolution (the aqueous solution) by the amount previously described. Atthe same time the extractant content of the extraction solution isincreased to the extent that the mass flow of the extraction solutionstays unchanged or increases a little. Thus the viscosity of theextraction solution can be raised successfully.

The factor by which the extractant content is raised compared with thenormal recommendation in the method according to the present invention,varies between 1.2-5, and is preferably between 1.5-3. When very dilutecopper-containing feed solutions with max. 2 g/l of copper are beingtreated, the factor may always rise to 5 i.e. according to our inventionthe extractant content would then be of the order of 7-25 vol. %,preferably 15-25 vol. %. When the feed solution copper content isbetween 2-4 g/l, the preferred extractant content is in the range of15-30 vol. %. Generally, however, the extractant content does notincrease above a content of 30% by volume. The viscosity of theextraction solution in this case rises to between 3-7 cP, which isenough to raise it to a clearly higher level than the viscosity of theaqueous solution. Normally, the aim is to achieve an O/A viscosity ratioof between 1.2-3, preferably 1.5-2. According to the invention, whenextracting dilute copper solutions the extractant content in theextraction solution is presently set in the range of 7-30 vol. %,preferably 15-30 vol. %.

Regarding aqueous solutions containing over 4 g/l of copper, even anordinary extractant content in the extraction solution gives a fairlygood result. For these solutions, the use of an extractant factor of1.2-2.0 times the recommendation improves the mixing durability of thedispersion. With the method according to the invention, however, it ispossible to raise the extractant content in the extraction solution to25-50 vol. %, when the copper content of the aqueous solution is 4-8 g/land even up to 40-70 vol. % if the copper content of the solution isover 8 g/l. The viscosity of the extraction solution can also be raisedpartly or wholly with the use of a diluting agent. The distillationrange and viscosity of the diluting agents generally used was mentionedearlier as being rather low. If other diluting agents are used, this canalso raise the viscosity of the extractant. Alifatic hydrocarbonproducts can be chosen with a distillation range in the range of220-275° C. or 240-270° C., and the viscosity of these substancesmeasured at a temperature of ±25° C. is 2.7 or 3.2 cP. If it is desiredto use aromatic hydrocarbons, the viscosity of hydrocarbons with adistillation span of 230-290° C. is about 3 cP. It is also possible touse mixtures of alifatic and aromatic hydrocarbons.

When treating dilute aqueous solutions containing less than 4 g/l ofcopper, there is a possibility in our invention of using hydrocarboncompounds that boil at a high boiling range as the diluting agent. Theuse of a diluting agent to increase viscosity is preferred since thediluting agent is always cheaper than the actual extractant. Theproportion of diluting agent in the extraction solution can be between30-93%. It is easier to achieve the required rise in viscosity withoutthe density of the extraction solution increasing significantly withalifatic hydrocarbons. The use of alifatic hydrocarbons is alsorecommended for reasons of industrial hygiene.

It was mentioned above that when raising the viscosity of the extractionsolution it is possible to decrease the external pumping of theextraction solution coming to the extraction stage from outside. If therise in viscosity takes place with an extraction solution dilutingagent, it is not possible to decrease pumping. On the other hand, whenviscosity is raised with an extractant, xternal pumping of theextraction solution can be reduced significantly compared with theamount of copper-containing aqueous solution being conveyed to theextraction stage. If viscosity is raised both by increasing theextractant content and by using the aforementioned diluting agent, theamount of external pumping decreases in the same degree as theextractant content is increased.

The method according to our invention is described in the attacheddrawings, where

FIG. 1 shows a schematic view of the equipment used in the method of thepresent invention,

FIG. 2 shows a stage calculation of the prior art, where the coppercontent of the aqueous solution (PLS=pregnant leach solution) coming tothe extraction stage is 1.5 g/l and the extractant content of theextraction solution is 5 vol. % Acorga M 5640,

FIG. 3 shows a stage calculation according to the present invention,where the copper content of the PLS is 1.5 g/l and the extractantcontent of the extraction solution is 15 vol. % Acorga M 5640,

FIG. 4 shows a stage calculation according to the present invention,where the copper content of the PLS is 1.5 g/l and the extractantcontent of the extraction solution is 25 vol. % Acorga M 5640,

FIG. 5 shows a stage calculation according to the prior art, where thecopper content of the PLS is 3.0 g/l and the extractant content of theextraction solution is 8.5 vol. % Acorga M 5640,

FIG. 6 shows a stage calculation according to the present invention,where the copper content of the PLS is 3.0 g/l and the extractantcontent of the extraction solution is 15 vol. % Acorga M 5640,

FIG. 7 shows a stage calculation according to the present invention,where the copper content of the PLS is 3.0 g/l and the extractantcontent of the extraction solution is 25 vol. % Acorga M 5640,

FIG. 8 shows a stage calculation according to the present invention,where the copper content of the PLS is 6.5 g/l and the extractantcontent of the extraction solution is 22 vol. % Acorga M 5640,

FIG. 9 shows a stage calculation according to the present invention,where the copper content of the PLS is 6.5 g/l and the extractantcontent of the extraction solution is 30 vol. % Acorga M 5640,

FIG. 10 shows a stage calculation according to the present invention,where the copper content of the PLS is 6.5 g/l and the extractantcontent of the extraction solution is 40 vol. % Acorga M 5640,

FIG. 11 shows a stage calculation according to the present invention,where the copper content of the PLS is 2.5 g/l and the extractantcontent of the extraction solution is 40 vol. % LIX 984N, and

FIG. 12 shows a stage calculation according to the present invention,where the copper content of the PLS is 32 g/l and the extractant contentof the extraction solution is 50 vol. % Acorga M 5640.

FIG. 1 describes a copper extraction process for treating dilute coppersolutions. The process consists of two extraction stages, E1 and E2, oneextraction solution washing stage W and one extraction solutionstripping stage S. Both the extraction stages and the washing andstripping stages consist of a mixing section 1, a settler 2, and a pump3 used to transfer the dispersion. The mixing section has at least onemixer, which is preferably equipped with the mixing devices describedearlier. The principles of the extraction stages are the types describedin e.g. WO patent application publications 97/40899, 97/40900, 97/40901and 97/41938.

As usual, the extraction functions on a counterflow principle, wherebyaqueous solution 4 comes first to extraction stage E1 and extractionsolution 5 to stage E2. The aqueous solution exiting the finalextraction stage E2, raffinate 6, is fed back to ore leaching, andcopper-enriched extraction solution 7 is fed from E1 to washing W andstripping S. In practice, the extraction solution is circulated viastorage tanks. Lean lectrolyte 8 is fed from electrolysis to thestripping stage where the copper contained in the organic phase isextracted. The aqueous solution 9 containing copper sulphate exiting thestage goes as rich electrolyte to electrowinning and the strippedorganic phase 5 is circulated back to extraction stage E2.

FIG. 1 shows how considerably the size of the washing and strippingstages of the extraction process is reduced when an extractant is usedaccording to the invention to raise the viscosity of the extractionsolution. In fact the reduction is in direct ratio to the externalextraction solution pumping, because the mixer-settlers in question aredimensioned directly with the solution flows in all respects, pumping,mixing and solution separation.

Therefore, in cases where the extractant content is raised for exampleto double the amount normally used, and external extraction solutionpumping is correspondingly decreased to half the normal flow, the mixerand settler volumes of the washing and stripping stages are halved. Theactual extraction stages E1 and E2 remain almost their earlier size andthe same external extraction solution pumping goes through them, but theextraction solution can be circulated within the stages in order tomaintain extraction solution continuity. The extraction solutions flowthrough each stage of the extraction equipment at essentially the sametime. As mentioned above, the O/A mixing ratio of the solutions may bereduced according to the method of the invention to below 1 to a valuebetween 0.7-1.0, and the size of the extraction stages equipment can bereduced correspondingly.

When estimating the effect of our invention on the size of theextraction equipment, it should be noted that FIG. 1 is only indicativeof the relative size of the extraction stages and that of the washingand stripping stages. There are often two stripping stages in anextraction plant and in some cases also two washing stages. Then thesavings made by reducing the size of the equipment are correspondinglygreater. The amount of extraction solution inside the extraction plantis also reduced correspondingly even if the changes in the amount ofextractant itself are not large, since the content of extractant in theextraction solution has been raised. In certain cases it is expedienteven to raise the amount of extraction agent circulating in the process,so that the advantages described in the method can be achieved in fullmeasure.

The method according to our invention provides the opportunity to treatdifficult impurities such as copper ore containing chloride, nitrate ormanganese in an economical way. In particular, ores containing a lot ofiron are generally problematic, because iron increases the transfer ofthe above-mentioned impurities to the electrolyte via the extractionsolution. This results in a situation where it is even more importantthan before to prevent the transfer of said impurities first to theextraction solution with the unseparated drops of aqueous solution fromextraction stage E1 to washing stage W and from there on to strippingstage S.

According to our invention it is now possible to use equipment that issmaller than usual in the washing stage, but as it is known on the otherhand, a prolonged settling time in the washing stage (larger settler)improves the separation of impurities. Now it is possible to enlarge thewashing stage, in particular its settler section in relation to theextraction solution flow used, for instance the size of a settleraccording to the conventional method without increasing costs and toachieve better separation of impurities than before. In practice thismeans that in the washing and stripping stages the mixing and separatingtimes are longer, i.e. the solutions flow through them more slowly thanthrough the actual extraction stages. With this system our method offersthe possibility for flexible, case-specific dimensioning.

When poor copper ores are processed by direct leaching, the result, asstated above, is an aqueous solution with a copper content in the rangeof 1-4 g/l, and in addition neutral salts accumulate in the solution.The sulphate content of the solution may rise to between 40-120 g/l,which causes a rise in the viscosity of the aqueous solution, but on theother hand, sulphate has the benefit of acting as a pH buffer when usingcopper extraction in the pH range of 0.8-2.2. In other words it improvesthe equilibrium of the copper extraction and makes more copper transferto the extraction solution.

EXAMPLE 1

A series of tests were carried out, which show that the separation ofthe organic solution and the aqueous solution from each other improveswhen the viscosity of the organic phase is raised by increasing theextractant content in copper extraction according to our invention.Table 1 presents the composition of the extraction solution and theresults obtained.

The aqueous solution was made using ion-exchanged water, copper sulphateand sulphuric acid. The copper content of the solution was 2 g/l, thesulphate content 52 g/l and the pH 1.8. The extraction solution wasprepared by mixing the commercial extractants shown in the table indifferent proportions with a commercial kerosene solution D70 asdiluting agent. Mixing contact was made between the extraction solutionsand the copper sulphate solution (aqueous solution) at room temperatureand in the O/A phase ratio of 1.0, thereby obtaining the copper contentvalues of the solutions in the table. After mixing all the solutionswere recovered and stored for two weeks before the actual mixing tests.This ensured that the extraction solutions in particular corresponded tothe solutions used in normal extraction, without the drawbacks of newextraction solutions.

A double helix agitator as described in U.S. Pat. No. 5,185,081, with adiameter of 152 mm and height of 174 mm was used in the mixing tests.The mixer itself was a flat-bottomed cylinder with a diameter of 214 mmand effective solution depth also of 214 mm. The cylinder was equippedwith four baffles positioned on the frame of the cylinder, with a widthof 18 mm and at a distance of 3.5 mm from the inner surface of thecylinder.

The mixing contact itself was made at room temperature and in the O/Aphase ratio of 1.0 so that the extraction solution was continuous in alltests and the aqueous solution in drops. The revolution speed of themixer was 220 rpm and the duration of mixing was 3 minutes in all tests.In all tests each extraction solution was mixed with a new batch of theaqueous solution. After mixing the solutions were made to separate bythe effect of gravity. 15 minutes after mixing the amount of residuesolution in each of the separated solutions was determined. The dropresidues (entrainment levels) are shown in Table 1, where A/O meanswater in the extraction solution and O/A means organic phase drops inthe aqueous solution.

TABLE 1 Residual drops Extr. sol. Visces. Cu/extr. sol. A/O O/A TestExtractant til.-% Dil. agent til.-% cP g/l ppm ppm 1 Acorga M5640 5 D7095 2,7 2 500 90 2 Acorga M5640 8,5 D70 91,5 3 3,5 460 70 3 Acorga M564015 D70 85 3,3 6,2 150 40 4 Acorga M5640 25 D70 75 4,2 7,4 100 25 5Acorga M5640 30 D70 70 4,9 13,7 150 25 6 LIX994N 40 D70 60 6,1 19,8 5015 7 Acorga M5640 50 D70 50 8,2 20,1 50 12

The tests show that raising viscosity by increasing the extractant(extraction reagent) content clearly decreases the amount of residualdrops in the settled solutions.

EXAMPLE 2

An aqueous solution was prepared with a copper content of 1.5 g/l,sulphate content of 50 g/l and pH of 1.8. Three different extractionsolutions were also prepared:

1. Acorga M5640 5.0 vol.-% D70 95 vol.-% 2. Acorga M5640 15.0 vol.-% D7085 vol.-% 3. Acorga M5640 25.0 vol.-% D70 15 vol.-%

The first solution represents an extraction solution according to theprior art.

Extraction equilibrium curves EEQ and stripping equilibrium curves SEQshown in FIGS. 2, 3 and 4 were defined for the extraction solutions andaqueous solutions in question with the method used by experts in thisfield. Diagram 2 shows the prior art, diagrams 3 and 4 the methodaccording to this invention. Next, making use of the equilibrium data inquestion, an extraction calculation was made for a copper extractionprocess with two extraction stages functioning on the counterflowprinciple and two stripping stages. The calculation was made on thebasis of the McCabe-Thiele method, familiar to specialists in the field.The extraction and stripping stages reach as far as the equilibriumcurve, because the stage efficiency is very high when using for instancethe equipment described in WO patent publications.

The three stage calculations presented in the example show that thecopper extraction yield remains at a good level and almost unchanged,even though the external pumping of the extraction solution is reduced.The copper contents of the raffinate are in all cases 0.2-0.4 g/l. Thelowest cont nt is obtained by raising the extractant content to 15%,whereby the external pumping of the extraction solution can be reducedto 35% of the PLS (pregnant leach solution) feed i.e. copper-containingaqueous solution feed. It is apparent from the stage calculation inquestion that the extraction equilibrium remains good in extractionconditions (the EEQ curve rising steeply when the Cu content of theaqueous solution is under 0.5 g/l) over its extraction solution coppercontent level, set for the extraction solution after the secondstripping stage S2 (dotted line BO, e.g. 3.0 g/l in FIG. 3).

Another essential factor is that the stripping equilibrium allows themaking of strong copper electrolyte when the copper content of theextraction solution can be lowered sufficiently. This means the levelwhere the extraction equilibrium is still rising sharply in an aqueoussolution Cu content of under 0.5 g/l, as stated earlier. The stagecalculation reveals that with the method according to the presentinvention, a significant improvement is achieved in the copper contentof the electrolyte going to copper electrolysis. With two strippingstages the electrolyte was made almost saturated as regards coppersulphate.

In different stage calculations the copper electrolyte developed asfollows: in a normal copper process (extractant content 5 vol. %) thecopper content of the “poor” electrolyte (LEL=lean electrolyte) comingto the washing stage is to be kept as low as 34 g/l and in the “rich”electrolyte (REL=rich electrolyte) the content may rise to the value of42.5 g/l. In the present method the corresponding values are 36 g/l and50 g/l when using an extractant content of 15 vol. % and 36 g/l and 51.5g/l when using an extractant content of 25 vol. %.

In the method according to the present invention a smaller amount thanusual of extraction solution is circulated in relation to the PLSsolution. Likewise the electrolyte circulation is correspondingly muchsmaller. In order to describe the information included in the stagecalculations the circulation of the solutions can be checked forinstance on the basis of diagram 3. The stage calculation is in twoparts: extraction on the left and stripping on the right. The solutioncompositions of the different stages can be seen at the intersectionpoints of the stages and the equilibrium curves. For example, inextraction stage E1 the Cu content of the aqueous solution decreasesfrom the PLS content of 1.5 g/l to 0.6 g/l and the Cu content of theextraction solution rises from the E2 content of 4.2 g/l to 6.7 g/l. Instripping stage S1 the extraction solution on the other hand falls froman LO (loaded organic) value of 6.7 g/l to 4.2 as the Cu content of thecopper electrolyte rises from 40.4 g/l to 50.0 g/l. The Cu content ofthe extraction solution falls further to a BO (barren organic) value of3.0 in stripping stage S2, from where the extraction solution moves onto extraction stage E2 of the extraction.

The important points in said stage calculations are the so-calledoperating lines which indicate the contents in which the solutions toucheach other when entering or leaving the first extraction and strippingstages E1 and S1 and the final extraction and stripping stages E2 and S2and in between said stages. From the nature of the stage calculations itfollows that the gradient of the operating lines indicate the externalsolution pumping i.e. the ratio of PLS and extraction solution flows inextraction as well as the ratio of electrolyte and extraction solutionflows in stripping. It has been possible to calculate from the externalpumping ratios how much the electrolyte circulation is reduced with ourmethod in relation to the amount of PLS flow.

Certain figures characteristic of our invention have been assembled inTable 2, when the extractant contents of the extraction solution are 15and 25 vol. % and these figures are compared with figures forconventional copper extraction, where the extractant content is 5 vol.%. The copper content of the aqueous solution (PLS) is 1.5 g/l in allcases. The extractant is Acorga M5640 and the diluting agent keroseneD70. The temperature of the extraction solution is 18° C.

TABLE 2 Quantity Kuva 2 Kuva 3 Kuva 4 Extractant content, vol-% 5 15 25Viscosity of extraction solution, cP 2,7 3,3 4,2 Cu content ofraffinate, g/l 0,3 0,2 0,4 Rise in Cu content of extraction solution,g/l 1 3,7 4,9 Rise in Cu content of electrolyte, g/l 8,5 14 15,5 Richelectrolyte content, g/l 42,5 50 51,5 Ext. solution pumping ratio in 1,20,35 0,24 extraction O/A Ext. solution pumping ration in 8,5 3,8 3,2stripping O/A Flow ratio of electrolyte and PLS 0,14 0,09 0,08

From this table the advantages given by our invention are apparent. Inaddition to the raised viscosity of the extraction solution and the factthat the solutions can be separated cleanly, it has been possible toreduce essentially the size of the equipment for handling the extractionsolution in the extraction process, such as washing and strippingequipments, as well as other extraction solution equipment for theexternal circulation of the extraction solution, such as storage tanksand post-separators for separating the residue solutions. Likewise thesize of the equipment for handling the electrolyte is reduced, such asflotation and pressure filtration apparatus, any possiblepost-separators and storage tanks. Another important factor is that thecopper content can be raised, ensuring the quality of the copper.

EXAMPLE 3

In this example the performance values according to the prior art areshown in diagram 5 and the values of the method according to the presentinvention in diagrams 6 and 7, based on the presented stagecalculations. These again show that the method helps reduce the size ofthe equipment considerably. The copper content of the aqueous solutionis 3 g/l, i.e. still a dilute solution. The extractant content of anordinary solution, given first in the table, is 8.5 vol. % and thefollowing 15 and 25 vol. % according to this invention, as in theprevious example. The extractant and diluting agent used are the same asin example 2. The temperature of the extraction solution is 18° C.

TABLE 3 Quantity Kuva 5 Kuva 6 Kuva 7 Extractant content, vol-% 8,5 1525 Viscosity of extraction solution, cP 3 3,3 4,2 Cu content ofraffinate, g/l 0,3 0,25 0,35 Rise in Cu content of extraction solution,g/l 2,4 4,5 6,3 Rise in Cu content of electrolyte, g/l 9,5 14 15,5 Richelectrolyte content, g/l 45,5 50 51,5 Ext. solution pumping ratio in1,13 0,61 0,42 extraction O/A Ext. solution pumping ration in 3,96 3,112,46 stripping O/A Flow ratio of electrolyte and PLS 0,29 0,2 0,17

EXAMPLE 4

In this example, an aqueous solution was used with a Cu content of 6.5g/l, in other words richer than is usually achieved with direct leachingof any poor ore. However, even when treating this kind of solution ourmethod has distinct advantages. In the next table the stage calculationsof diagrams 8, 9 and 10 were used. The contents of the extractionsolution are 22, 30 and 40 vol. %, the extractant Acorga M6540 and thediluting agent again kerosene D70. The temperature of the extractionsolution was 18° C.

TABLE 4 Quantity FIG. 8 FIG. 9 FIG. 10 Extractant content, vol-% 22 3040 Viscosity of extraction solution, cP 3,7 4,9 6,3 Cu content ofraffinate, g/l 0,2 0,3 0,4 Rise in Cu content of extraction solution,g/l 5,9 9,2 14,5 Rise in Cu content of electrolyte, g/l 16 16 16 Richelectrolyte content, g/l 52 52 52 Ext. solution pumping ratio in 1,070,67 0,42 extraction O/A Ext. solution pumping ration in 2,71 1,74 1,1stripping O/A Flow ratio of electrolyte and PLS 0,4 0,39 0,38

EXAMPLE 5

This example studied the possibility of reducing the external pumping ofthe extraction solution considerably by raising its extractant contentto a significantly high level. When the pH of the base solution is closeto 2 and the same aqueous solution contains sulphates, the extractionequilibrium is very beneficial when the copper content of the aqueoussolution is low. In the case of the example the Cu content of theaqueous solution is 2.5 g/l, the pH is 1.8 and the amount of sulphates50 g/l. According to this example the method of the present inventionincreases the copper extraction yield. As shown by the stage calculationin FIG. 11, a very low raffinate content of 0.15 g/l copper is obtainedwhile the external pumping of the extraction solution ratio drops to aslow as 0.15. The external pumping of the electrolyte in ratio to theexternal pumping of the PLS also settles at the same value of 0.15. Inthis example the extractant used was the commercial chemical LIX 984N,which is similar to the reagent used in the previous example, and againkerosene D70 was the diluting agent. The extractant content was 50 vol.%.

TABLE 5 Quantity FIG. 11 Viscosity of extraction solution, cP 8 Cucontent of raffinate, g/l 0,15 Rise in Cu content of extractionsolution, g/l 15,7 Rise in Cu content of electrolyte, g/l 16 Richelectrolyte content, g/l 52 Ext. solution pumping ratio in extractionO/A 0,15 Ext. solution pumping ration in stripping O/A 1,02 Flow ratioof electrolyte and PLS 0,15

EXAMPLE 6

The example shows how high the copper content of the PLS can be raisedusing our invention. In this example the Cu content of the PLS wasraised up to 32 g/l while the extractant content of the extractionsolution was raised to 50 vol. %, with Acorga M5640 as reagent andkerosene D70 as diluting agent. Mixing with the double helix mixermentioned above is successful, even though an extractant content of asmuch as 40-70 vol. % is used. It is advantageous to do this when it isdesired to reduce external pumping of the extraction solution. The stagecalculation concerning 50 vol. % in FIG. 12 and the summary in Table 6clarify these possibilities further.

TABLE 6 Quantity FIG. 12 Viscosity of extraction solution, cP 8,2 Cucontent of raffinate, g/l 5 Rise in Cu content of extraction solution,g/l 13 Rise in Cu content of electrolyte, g/l 16,5 Rich electrolytecontent, g/l 50,5 Ext. solution pumping ratio in extraction O/A 2,07Ext. solution pumping ration in stripping O/A 1,27 Flow ratio ofelectrolyte and PLS 1,63

What is claimed is:
 1. A method for liquid-liquid extraction of copperfrom an aqueous solution containing more than about 40 g/l of sulphatesthe method comprising feeding an organic extraction solution and saidaqueous solution into a plurality of extraction stages, said extractionsolution containing an extractant, extracting copper in said extractionstages from said aqueous solution in the presence of said organicextraction solution by raising the viscosity of said organic extractionsolution to a range of 3-11 cP and dispersing the aqueous solution intodrops in the extraction solution while adjusting the volumetric ratio ofthe extraction solution to the aqueous solution to between 0.7-1.0.
 2. Amethod according to claim 1, wherein the viscosity of the extractionsolution is raised by raising the content of the extractant in theextraction solution.
 3. A method according to claim 2, wherein theviscosity of the extraction solution is raised by regulating theextractant content of the extraction solution in the range of 15-70 vol.%.
 4. A method according to claim 3, wherein said aqueous solution has acopper content up to about 2 g/l, and the viscosity of the extractionsolution is raised by adjusting the content of the extractant in theextraction solution to the range of 15-25 vol. %.
 5. A method accordingto claim 4, wherein the external pumping ratio of the extractionsolution and the aqueous solution fed into the extraction stagesadjusted to the range of 0.2-0.5 and the ratio between a stripped copperelectrolyte and the aqueous solution of the extraction is adjusted tothe range of 0.08-0.2.
 6. A method according to claim 3, said aqueoussolution has a copper content of 2-4 g/l, and the viscosity of theextraction solution is raised by adjusting the content of the extractantin the extraction solution to the range of 15-30 vol. %.
 7. A methodaccording to claim 6, wherein the external pumping ratio of theextraction solution and the aqueous solution fed into the extractionstages is adjusted to the range of 0.3-0.7 and the ratio between astripped copper electrolyte and the aqueous solution of the extractionis adjusted to the range of 0.15-0.25.
 8. A method according to claim 3,said aqueous solution has a copper content of 4-8 g/l, and the viscosityof the extraction solution is raised by adjusting the content of theextractant in the extraction solution to the range of 25-50 vol. %.
 9. Amethod according to claim 8, the external pumping ratio of theextraction solution and the aqueous solution fed into the extractionstages is adjusted to the range of 0.4-0.8 and the ratio between astripped copper electrolyte and the aqueous solution of the extractionis adjusted to the range of 0.25-0.50.
 10. A method according to claim3, said aqueous solution has a copper content of over 8 g/l, and theviscosity of the extraction solution is raised by adjusting the contentof the extractant in the extraction solution to the range of 40-70 vol.%.
 11. A method according to claim 10, the ratio of the extractionsolution and the aqueous solution fed into the extraction stages isadjusted within the range of 1-4 and the ratio between a stripped copperelectrolyte and the aqueous solution of the extraction is adjustedwithin the range of 0.8-3.
 12. A method according to claim 1, whereinthe ratio between the organic solution and the aqueous solution fed intothe extraction stages from outside is regulated in the range of 0.15-1.13. A method according to claim 1, wherein the viscosity of theextraction solution is raised by using aliphatic hydrocarbons, with aviscosity of 2.7-3.2 cP when measured at ambient femperature, asdiluting agent for the extraction solution.
 14. A method according toclaim 1, wherein the viscosity of the extraction solution is raised byusing aromatic hydrocarbons, with a viscosity of about 3 cP whenmeasured at ambient temperature, as diluting agent for the extractionsolution.
 15. A method according to claim 1, wherein the viscosity ofthe extraction solution is raised by using a mixture of aliphatic andaromatic hydrocarbons, with a viscosity of minimum 2.7 cP when measuredat ambient temperature, as diluting agent for the extraction solution.16. A method according to claim 1, wherein the sulphate content of theaqueous solution fed to solvent extraction is a minimum of 40 g/l.
 17. Amethod according to claim 1, wherein the extracting solutions flowthrough each extraction stage at essentially the same time.
 18. A methodaccording to claim 1, wherein the method further includes washing andstrippiing stages and the extracting solutions flow through the washingand stripping stages more slowly than the actual extracting stages.